Amplifiers and oscillators capable of operating at and above 100 GHz (to approximately 300 GHz) are not available if it is required that they be solid state, fully compatible with monolithic technology, efficient so as to minimize DC dissipation losses, and introduce only small to moderate noise levels into the RF spectrum. Conventional devices which can function at or above 100 GHz as oscillators or reflection amplifiers are IMPATT (and related carrier avalanche devices) and TED or Gunn diodes. IMPATT's, based on impact ionization generation of carriers by carrier collisions with the lattice, are low efficiency (on the order of 10%), high dissipation, devices which are also very noisy because of the collisional scattering behavior. They do, however, operate up to several hundred gigahertz (roughly 300 GHz) depending upon the circuit load, bias conditions, and device structure and material (e.g., Si, Ge, GaAs, InP). TED's, or Gunn diodes, (accumulation, dipole, and LSA modes of operation) are based on the transfer of electrons between two non-equivalent valleys in energy-momentum space. These devices are also low efficiency, high dissipation devices, but exhibit considerably lower noise measure (by 20 dB) than for IMPATT devices and can be realized in III-V periodic table elemental compound combinations. Such binary combinations include GaAs and InP. Other more complex compounds like ternary combinations are also possible, for example. TED's, unfortunately, appear to have a maximum operating frequency of about 150 GHz. Other devices related to the IMPATT, like the TRAPATT and BARITT, suffer from, respectively, low frequency operation (on the order of 10 GHz), and lower power (and efficiency).
Two other classes of devices which have been applied to low frequency or microwave applications (and sometimes millimeter wave frequencies) but which seem to be coming up in maximum operating frequency, are respectively the bipolar transistor and FET device. The bipolar transistor (including the heterojunction type), is a two carrier transport device, minority carrier controlled, and limited to frequencies below about 20 GHz. FET's, the other class of devices which has three terminals, have their behavior based on field effect and majority carrier transport. FET devices include the subgroups JFET's, MISFET's, and MESFET's. The JFET,, which controls carrier flow in a channel with a rectifying junction, is a low-frequency device (e.g., using Si or heterojunction semiconductors). MISFET devices (e.g., using Si or GaAs), which rely on channel control using a metal/oxide gate (enhancement and depletion mode of operation), are limited to frequencies under 10 GHz. MESFET's (e.g., using Si, GaAs, or InP), which depend on channel control employing a Schottky/semiconductor barrier gate, appear to be restricted to maximum operating frequencies of 80 GHz (GaAs) or 130 GHz (InP) with low noise production compared to IMPATT's or TED's. Best MESFET results to date have been obtained with state-of-the-art reproducible 0.25 .mu.m gate length devices. HEMT's, high electron mobility MESFET's using heterostructure layers to create 2-dimensional sheets of carriers, do not seem to offer substantial improvements to the ordinary MESFET maximum operating frequency.
Because of the deficiencies of the above-discussed conventional solid state devices for acceptable operation in the millimeter wave frequency regime, some prior art work has been done on alternative structures with distributed electromagnetic circuits interacting with carriers located in a semiconductor. Previously, such distributed structures (which have been fabricated and experimentally tested) have been solid state traveling wave amplifiers (SSTWA's) in analogy to the traveling wave tube (TWTA), with the exception of one device (a solid state grating amplifier or SSGA) which is in the form of a grating introducing spatial harmonics into the physical quantities to obtain amplification. To applicant's knowledge, such SSTWA's used continuous metal microstrip electromagnetic circuit structures which may all have large DC (static) potential and field build-up in localized regions under periodic circuit fingers, possibly severely limiting their operation as amplifiers; such SSTWA's were studied at cooled temperatures; and none of these SSTWA's have displayed any net gain. Recently, efforts have been made to DC isolate the periodic circuit fingers. However, little discernable electronic gain has been realized in doing this.
The above-mentioned solid state grating amplifier (SSGA) is comprised of a microstrip interdigitated finger structure with the fingers all DC isolated from each other, using input and output microstrip feeds. Such an SSGA structure appears to have produced only a small electronic gain.
None of the above-discussed prior art devices has used monolithic semiconductor integrated circuit technology.